A swash plate angle sensor for detecting an angle of a swash plate is provided to electronically control a hydraulic pump. A pump control unit calculates a discharge flow rate of a pump by using the detected swash plate angle to calculate a pressure command value of the hydraulic pump, and issues a command. However, when the swash plate angle sensor breaks down, the pump control unit cannot recognize a discharge flow rate of the pump. Accordingly, since the pump control unit cannot calculate a pressure command value, the pump control unit generally outputs a pressure arbitrarily set in advance, that is, a pressure setting value as a command.
However, in this case, when a load pressure applied to an actuator of the construction machine is higher than the pressure setting value set in the hydraulic pump, the actuator cannot be operated. In contrast, when the pressure setting value is higher than a load pressure, a required flow rate becomes larger. Accordingly, a discharge flow rate of the pump increases, and thus an absorption torque value of the pump also increases. In the latter case, if an absorption torque value of the pump becomes larger than a maximum torque value of the engine, a phenomenon of stopping the engine occurs.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.